Piston



Nov. '12, 1940. Y 0. BERRY PISTON- Filed Nov 20', 1957 2 Sheets-Sheet 1 INVENTOR. Orv-o Chev-E1 5522:;

ATTORNEYS.

Nov. 12,1940. 7 QQ ER YI 2, 21,535

PISTON Filed Nov. 20, 1937 2 Sheets-Sheet 2 Li; a I 12 11 INVENTOR. OTTO CA are? 51mm;

. ATTORNEYS.

Patented Nov. 12, 1940 umigso STATES PATENT OFFIICE 5 Claims.

This invention relates to pistons for internal combustion engines, and more especially to those made of aluminum or of an alloy in which the principal ingredient is aluminum.

The main objects of this invention are the following:

a. To keep the piston rings cooler than is possible under the same operating conditions in the aluminum pistons now in common use.

b. To keep the piston head as cool as is prac-- tical in an aluminum piston under the required operating conditions.

0. To improve the control by the piston of the amount of oil used by the engine.

In carrying out these main objectives, the following have taken form as auxiliary objects of the invention:

d. To divide the heat-flow from the piston head into two parallel paths, leading to the piston skirt and to the piston-ring flange respectively, and to control that division so that the heat-flow to the piston-ring flange can not become excessive.

e. To provide a piston skirt which-is able to receive a large amount of heat from the head and dissipate that heat, but which nevertheless is of a size such that said piston skirt may be made a close fit in the cylinder of the engine with complete assurance that it will never becometoo tight.

I. To provide in the skirt of an aluminum piston control bands on which the aluminum will slip easily while still fitting closely on the control bands; and to provide a method for ensuring that capability of easy slipping.

g. To provide between the piston head and the piston skirt a connection of such nature that the skirt will remain round whether the head be hot or cold.

h. To provide a piston that in addition to having the preceding characteristics is strong and rugged.

As a result of the combined efforts of a number of inventors, aided by the experience of the automotive industry through the years, it is possible to produce aluminum-alloy pistons which 'may be made a close fit in the cylinders, and which will maintain their clearance from the cylinders substantially unchanged throughout the temperature changes met in practice, without slapping, binding, scoring, or undue wear. In all these pistons this result is obtained by partially separating the piston skirt from the piston head, thus reducing the amount of heat that can flow from the piston head to the piston skirt, and by providing a skirt that will not become too tight under these conditions that are highly favorable for theskirt. It is characteristic of these pistons, however, that the rings tend to become too hot when the engine is running at high speed, and that when the engine becomes somewhat worn 5 the pistons allow it to use too much oil. These faults will be discussed separately.

The overheating of the piston rings and piston heads comes about as follows: In all the aluminum pistons now in use that do not slap when 10 cold nor get too tightwhen hot, it is a common characteristic, as already stated, that the piston heads are partially separated from the skirts. This reduces the amount of heat that can flow from the head to the skirt. The skirts are usually 15 ground oval, or cam-ground as the automotive engineer expresses it, so that the skirt is spaced away from the cylinder in the line of the pistonpin bosses. Besides the cam-grinding, the pistons are usually cast with a relief around the 20 piston-pin bosses that is often more than ninety degrees wide at the head end of the skirt. Very little heat can flow from the piston to the cylinder walls through these relieved areas. Yet the only place where the piston heads are joined to' 25 the skirts is in the region of the piston-pin bosses. The heat flowing from the piston head to the skirt is therefore not onlylimited by having a restricted path to follow, but it must also travel a long distance before it finally reaches 30 the cylinder walls of the engine. Thus in the present modern aluminum pistons the head from the head passes to the cylinder walls largely' through the ring-flange of the piston, and mostly through the rings themselves. The capacity of 35 the rings for handling heat is limited, however,

and under extreme conditions they and the piston heads become very hot. The ove'rheatingof the piston ringsand heads has become worse during the past few years. Engine designers have been studying how to shape combustion chambers so that they can use higher compressions without detonation. Petroleum refiners have also made marked improvements in their fuels, so that they will stand higher compressions. This situation has resulted in the common use of compression ratios in modern engines that are much higher than were formerly thought possible, and accounts for the fact-that much higher flame temperatures are being met now than ever before.

' Engines are also being run much faster than formerly. The oiling systems have been im-- proved, bearings made'larger and better, reciprocating parts lighter, and valves more heat-re- 2 sistant; and all of these thin have combined to make the higher speeds possible. These high speeds, together with the high compressions and high fiame temperatures, mean that heat is beingpoured 'into the. piston heads in modern automotive engines at a tremendously high rate. In the best of these engines, those giving the most power per cubic inch of piston displacement, it often happens that the ofl reaching the top rings not only becomes too thin to be a good lubricant, but is actually destroyed by the heat. This results in undue friction, rapid wearing of the cylinder walls, and scoring of the rings. One of the main objects of this invention, as previously stated, is to correct this over-heating of the piston head and more especially of the rings, so that the latter may be properly lubricated at all times.

Now for the fault of imperfect oil control on the part of a somewhat worn automotive engine.-

This is often accounted for as follows: It is now almost the imiform practice in these engines to supply oil to the main and connecting-rod bearings at a high pressure. When the engine is new and these bearings are a snug fit, only a reasonable amount of oil can flow through them and get onto the cylinder walls. The oil-control rings on the pistons cantake care of this amount of oil, and the'oil economy of the engine is good.

Whenthese bearings become wom and loose, however, the cylinder walls are flooded with oil. As previously stated, modern aluminum pistons have' cam-ground skirts, and/or large relieved areas which surroundthe piston-pin bosses :and

extend to 'the upper end of the piston-skirt. A portion of this excess oil often gets past these skirts where the cam-grinding or the relief spaces them from the cylinders. This overloads the oilcontrolrihgsonthepistonsahdcausestheengine to use too much ,oil'. One of the main objects of this inventionis, 50 correct this situation. I provide 'the piston time skirt that can safely be made round anda close fitin the cylinder of the engine.,-Whenthisskirtisproperlyfittedintoa whenitsbearing'sarelooseandthecylindersare at thesame time toward con-' it notonlymaybe and willremain round orsubstantiallysobut ex- ;pands andcontracts with-such a lower thermal 'eoeificientlof expansionwith respectto that of aluminum and its alloys that. proper clearance betweenthepistonskirtandthecylinderismaintainedatalltemperatures.

Other objects of my hereinafter.

invention will appear My inventionia" illustrated in the following drawings,'which invention in certain preferred forms. In such'idrawings, Fla. 1' ha longitudinal section. with parts in elevation, or a piston a form of my invention in.

which two expansion-control bands are used in the skirt, the skirt is provided with a single slot,

*and the heat-flow to the piston-ring belt is controlled withott requiring any groove in the piston-head surface; Figs. 2, 3, and 4 are transverse sections substantially on the lines 22, 3-3, and

H of Fig. 1; Fig. 5 is a longitudinal section,

which there are two expansion-control bands, and two slots in the piston skirt, and an annular groove in the piston head to reduce the crosssection of the heat-flow path to the piston-ring flange; Fig. 6 is a longitudinal section generally similar to Figs. 1 and 5 of a'piston embodying a form of my invention in-which there is only one expansion-control band and'in which the piston skirt has three slots; big. 7 is a fragmental crosssection, illustrating a' modification in which the two sides of a slot in the piston may be interconnected by a flexible connection; Fig. 8 is another longitudinal section and partial elevation generally similar to Fig. 1, of a piston embodying a form of my invention in which there are two.

bodying various modifications of my' invention; Fig. 13 is a transverse section on the line li-ll of Fig. 12; and Fig. 14 is a transverse section gen-' erallysimilartol 'ig. 13 butonasmallerscale,to illustrate a modification in which a split expansion-eontrol band with non-overlapping ends- 1s used.

A piston embodyin my invention, as illustrated in the various figures of the drawings, has a piston head 20, the top portion II of which is joined at its edge to a depending peripheral piston-ring flange. 22 provided with piston-ring grooves 23, a piston skirt 24, and piston-pin bosses 25 {which are desirably provided in and carried by the skirt. Both the head and the skirt are made of aluminum or aluminum-alloy. (collectively referred tosimply as aluminum) cast as one piece.

The piston skirt II has an upward extension 2-8, which extends upward from the cylinderengaging portion 21 from a point at or near the upper end of-the latter and lies radially inside of the piston-ring flange 22. The cylinder-engaging portion 21 of the skirt is preferably ground substantially round externally, especially in the region of the expansion-control bands hereinafter descrlbed, save that at and in the immediate vicinity of the 'piston-pin-bosses Iljthere maybe relief which desirably doesnot extendto either the top or the bottom of that. cylinder-bearing portionll. The upward skirt-extension 2', in the preferred embodiments of my invention, is

in general annular in cross-section,- as is clear from 2, and generslly cylindrical or slightly B conical; and it forms an integral and homogeneous connection between the top portion 2'! of the pistonhead-lland the cylinder-engaging skirtportion' 2]- by being castinon'e therewith; --'1'he.k wer edge of the flange 22 is spaced longitudinally from 'the'upper end of the mainjor cylinder-engaging skirtsportion 21, and

is spaced radially from the upward-skirt-extension 20, to provide a generally annular open space 2! which communicates with the exterior just below theedge of the piston ring flange 22 and is readily formed by the use of a sand core.

The upward skirt-extension 26 may join the main or cylinder-cumin! skirt portion 21 in various ways. For instance, it 'may spring inwardly directly from the upper end of that cylinder-engaging portion 21 and swing upward in a smooth curve into .the annular portion that joins the piston head, as is illustrated in Figs. 1, 6, 8, and 11: or it may spring inwardly directly from the upper end of that cylinder-engaging portion 21, but dip slightly downward first before swinging upward in a curve into the annular portion that joins the piston head, as is illustrated in Fig. 5; or it may spring inwardly from a point slightly below the upper edge of the cylinder-engaging portion 21 and swing upward into the annular portion that joins the piston head, as is illustrated in Fig. 10. v

The piston head 20 is composed of two sections, the more or less flat disk 2| forming the top portion, and the depending ring flange 22. The metal joining these two sections is made of constricted cross-section, markedly thinner than is either the top portion 2| or the upward skirt-extension 26, to make smaller the cross-section of the metal path for heat flowing from the top portion 2| to the piston-ring flange 22. This constriction may be provided by extending the open space 28 up fairly close to the upper surface of the piston head, to leave a constricted portion 30 to limit that heat-flow to the piston-ring flange 22, as is illustrated in Figs. 1, 6, 8, and 10. Or, if it is desired that the annular space shall not extend so close to the top surface of the piston, that top surface may be provided with an annular groove 3|, preferably slightly oblique to the piston axis, as is shown in Figs. 5and 11, which annular groove'lies generally above the upper end of the annular space 28 to leave between it and .that annular space the desired constricted portion 32. By controlling the depth of the groove 3!, which is commonly provided by machining, the size of the constricted portion 32 is readily controlled. If desired, the annular groove 3| may be filled with some suitable heat-insulating filling 33, such as asbestos, as is illustrated in Fig. 11; but that filling is not always necessary.

By reason of this construction, the heat which the piston head receives from the explosion may flow from that piston head in two paths in paral-;

lel. One path is by way of the constriction 30 or 32 (Figs. 1 and 5 respectively) to the ring flange 22, and therefrom through the piston rings into the cylinder and the cooling water in the water jacket. The other path is by Way of the upward skirt-extension 26 into the main or cylinder-engaging skirt-extension 21, and hence across the 'oil film into the cylinder and the cooling water.

' because they are not in the heat-flow path from the piston head to the cylinder-engagingportion 21 of the piston skirt.

The piston head expands and contracts upon changes in temperature in accordance with the thermal expansivity (thermal coeificient of expansion) of the aluminum alloy of which it is made. It is preventedfrom ever becoming too tight in the cylinder by being given an initial clearance larger than any expansion it can make. This is possible for the reason that the rings form the seal for this part of the piston, and it is not necessary that the ring-lands ever come close to the cylinder walls.

The problem in connection with the skirt is a different one. The cylinder of the engine is ordinarily made of cast iron, and is water-cooled.

That cast'iron has about half the thermal expansivity of the aluminum piston alloys, and never reaches a very high temperature. The piston skirts, on the other hand, are made of aluminum (or aluminum alloys), and in pistons after my design they handle a large amount of heat. This makes it necessary for them to become quite hot, especially at the upper or head end of the cy1inder-bearing portion. A comparatively small increase in the temperature of the skirt would cause the aluminum in it, if uncontrolled, to expand more than the allowable clearance between the cylinder and the piston of a cold engine. The expansion of the piston skirt upon increase in temperature must therefore be restricted to less than the expansionwhich would be produced by the thermal expansivity of aluminum alloy if proper clearance between the piston skirt and the cylinder is to be preserved at all temperatures; and more especially so as the piston skirt is preferably machined substantially round, with clearance at the piston-pin bosses only, instead of being ground oval. 1

To permit this, whenever substantially constant skirt clearance is desired, the piston skirt is provided with "one or more generally longitudinal slots, which can be closed to a greater or less extent by various expansion-restraining forces as the temperature of the piston skirt increases, thus making the skirt compressible ,in relation arranged, but there is at least one slot in this upward skirt-extension 26 and in at least the upper part of the main or cylinder-engaging portion 27. The slots can be and preferably are completely open, as illustrated in many of the figures of the drawings; but they may have their opposite edges interconnected, usually for only a portion of the slot-length, by a flexible connectio 33, as is illustrated in Fig. 7. i

In the embodiments of my invention shown in Figs. 1 to 4 inclusive, and Figs. 12, 13, and 14, there is a single slot 35 which extends throughout the entire length of the piston skirt, from the bottom thereof to substantially the point where the piston skirt joins the piston head 2| This slot 35 is desirably slightly oblique, at leastin the cylinder-engaging portion 21 of the skirt, to prevent the production of a ridge in the cylinder wall.

Inthe embodiments of my invention shown in Figs. 5 and 10, there are two slots, one being the oblique slot 35 (of Figs. 1 to 4) extendingthe full length of the piston skirt, and the other being a slot 36 which is located approximately opposite the slot 35 and extends from the upper end of the skirt-extension 26 downward through that skirt-extension and part way through the cylinder-engaging skirt-portion 21 to an intermediate point in the length of the latter, to end ina round hole 31. By having two slots the skirt is made less stiff.

Neither slot 38 nor slot 39, nor the two of them together, extends the full length of the piston skirt; but the slot 38 extends downward from 'cumferentially as is the slot 35 of Figs. 1 and 5.

the top of'the upward skirt-extension 26 through that skirt-extension and only a short distance downward into the main or cylinder-engaging to its diameter. The slot'or slots may be variously skirt-portion 21 to end in a round hole", and

the slot 39 extends upward from the bottom of the skirt a comparatively short distance to end in a round hole 4|. This arrangement of the 5 slots gives a fairly flexible skirt construction.

In the embodiment of my invention shown in Figs. 8 and 9, a slot 42 extends the full length of the piston skirt, as does the slot 36 in Figs. 1, 5, and 10; but it diiIers from the slot 36 in that it has two oppositely oblique portions, which is sometimes desirable. In addition to the slot 12, shown in this embodiment of myinvention, there may be a number of slots 43 extending longitudinally at least in the region where the two skirtportions 26 and 21 join each other, and desirably extending upward to or substantially to the top of the upward skirt-extension 26 and downward into the main or cylinder-engaging skirt-portion 21 to the vicinity of the piston-pin bosses 25. The

slots it are often conveniently all in planes parallel to the axis of the piston pin, to make it possible to withdraw the 1 cores when metal cores are usedto form the open interior of the piston:

P m l" I.-

r In the embodiment of inventionsshown in 11, asingles10t extends downward from the top of the shirt-extension It throush that skirt-extension a large part of the length of the main or'c'ylinderskirtportion 21, to terminate ina round hole ll iocated below the transverse plane of the pistonpin axis. I

By the provisionof these slots 35, 38, ll, II,

the main or cylindereengaging skirt-portion II is made compressible,either at its upper endor throughout its length asthe case may be. so that by the closingjof-ithoseslots when the'pistonqis 0 heated the expansionoLt e. skirt-diameter may be made independent of the of ton head and inf-the of sion of dialuminum-alloyg andmade bi u l t aw d- 4,5 trolled. If 'nojlo xtehjds" to the iowenmdof s r f r bl :sr und less than those the :tha't: owe

oval. I V The compressionlof f the mam-f 0.1 cyunderens s s skirt-portion; 11,, tes least of its upper end, called for by the thermal, suspensions: or aluminum-alloy, may if desired be merely bythe reaction'of the encircling cylinder wall: andf'that is the cs'se'in the embodiment of my invention showninFlg. 11; j H

However, in the preferred forms of my loverstion I control that expansion of the main or cyl inder-engaging skirt-portion 21, or at least of .theupper endthereof, by means independent oi '60 the cylinder wall, and embodied in and forming of the piston itself as is illustrated in. the other figures oi the drawings. To this end I'Provide in the upper end of the main or cylinderengaging skirt-portion 21 an expansion-control band It.- This expansion-control band may be this expansion-control band, as in Figs. 12, i3,-

" and 14, it is desirably remote fromany ofithe which metal are'convenientlyof the three:

l2, 4!, and M, or various combinations of -them,;v

perpendicular to the piston axis.

' By reason of the expansion-control band' Ill, the piston skirt in the plane of such expansioncontrol band is prevented from increasing in diameter too greatly upon increase in temperature: It is held down to the increase which is permitted by the thermal coefilcient of expansion of the expansion-control band. The excess expansion of the aluminum is taken up by circumierential movement of it on the expansioncontrol bandtoproduceagreater or lessclosing of the slot or slots 38, 30, II, 42, and/or 41 which cross the plane of that expansion-control band. This control is effected without material distortion of the circular form of the piston skirt by having the various parts of the piston designed to the-tend, and especially by reason of the annular form of the upward skirt-extension 28.

* TheeXpnnslOIi-cnntrul band II at the upper end of-the main or cylinder-engaging skirt portion 21 may be the only expansion-control band. as is the case in that form of my invention which is illustrated in Fla. 6. However, I deem it preterable to have a second expansion-control band 52 near the bottom of the piston skirt. as is illustrated in Figs. 1 and 4. 5, 8, 10, and 12. This-is shown assn endless band, although it is not necessarily so. v The lower expansion-control band I! may be of steel or nickel steel, with a less than that of aluminum or. aluminumailoyi; but the thermal expansivity or the lower expansiomcontrol band I! may be andis sirsb yir than that of the upper expansion-control it because the lower part of thepis'ton sklrtdoesnot get so'hot as the ma may be oi any desired vcross section. .1 cmi'slder it best tohave expansion-control band l'lr'sthcr radius of the piston, as

by being of a round or square cross-section, for it is this expansion-control band. which exerts most or thecontrol. The lower expansion-control bandll, the load on it is less, may

made of a steel strip which is fairlywide in the direction of the piston length and relativelys thin in the direction of the piston radius. Both expansion-control bands-ll and 82 are cast in place-my which I mean. that they areprefabricated and set in proper position in the mold into which the molten aluminum-alloy is poured to form the aluminum-alloy body of the piston.

' Toinsurethe boat control,- the expansion-control bands should meet two requirements. They should be cast in place in .theskirt in such a way that the aluminum will slide over them easily, and they should be a close ht in the aluminum. Untreated steel bands cast in place directly in the aluminum will not allow the latter to slip as readily as is desirable; for the aluminum gets too powerful a pinching grip on the steel bands. To-prevent this I provide the steel bands with a slip-promoting coating: for which 1 use ane!- be rubbedtremely flne soi't, unctuous, amorphous, powdered graphite, such as is frequently used as a coating on dry sand cores or on the surfaces of metal molds. I heat the bands well above the boiling temperature of water, and then apply to the bands, with a spray gun, a water suspension of that graphite. In this way I produce a thin bu fair y hard coating of the graphite thatis baked on to the bands and is hard enough so that the band may be handled without material danger of removing such coating. In fact, the coated bands will stand considerable handlin without having the coatings come all. This cost- In'gnan be made thick enough so that a the aluminum casting contracts in cooling. the graphite will be compressed without allowing the aluminum to grip the band too strongly, and yet thin enough so that the band will be a clos flt in the casting. The graphite not only prevents the casting from obtaining too powerful a grip on the band, but also serves as an excellent lubricant to facilitate the sliding of the aluminum .over the bands.

Other coatings may be used instead of the graphite, but care must be exercised to avoid the use of any substance that will. form a gas and produce blow-holes in the casting. graphite is likely not to cling to the bands in large enough quantities to prevent the gripping of the aluminum. A graphite paste is likely to form too thick aluminum too loose on the bands. Moreover, either dry graphite or graphite paste may often off fairly easily, and may thus allow the aluminum to grip the bands too strongly at I various points. I therefore prefer the coating reason of the bosses, a head 'castintothe upperpart.ofsaidskutinthere-' canbe of baked graphite applied as described.

Because a piston according to this invention ground roimd, instead of being around provides an imusually flne oil control. expansion-control band or hands, this grinding round may be made with confidence that it will not result in too tight a lit of the piston in the cylinder. no matter how hot the engine 88 I claim as myinvention:

1. A piston, comprising a skirt,

made up of a top portion and a ring flange, connecting means of large heatcarrying capacity that passes inside of said ring flange and joins said skirt to said top portion, said ring flange being Joined to said top portion by a section of metal markedly thinner than is the metal in said connecting means to keep small the heat-flow to the ring flange, and an expansion-control band that is of lower thermal exoval, it

a coating and so to make the.

piston-pin glen where it joins said connecting means, said skirt being provided with a plurality of longitudinal slots which extend across the plane .of said expansion-control band and which include slots which approach close to the piston head and slots which extend below the transverse plane in which the axis of the piston-pin bosses lies.

2. A piston comprising a skirt, pin bosses, at head composed of a top portion and a ring flange, and expansion-control bands having lower thermal expansivity than the skirt metal and mounted in the upper and lower parts of the cylinderengaging portion of said skirt, said skirt being separated from said ring flange and being-connected to the top portion of said head by an annular skirt-extension passing inside of said ring flange and being longitudinally slotted across the planes of said expansion-control bands, the upper expansion-control band having a lower thermal expansivity than has the lower expansion-control band.

3. A piston, comprising a head, pin bosses, and a skirt, said skirt being slotted longitudinally and having two expansion-control bands cast in place in it near the upper and lower ends of its cylinder-engaging portion, both of said expansion-control bands having a lower thermal expansivity than the skirt metal, and the upper one having a lower thermal expansivity than the lower.

4. A piston, comprising a skirt, pin bosses, a head made up of a top portion and a ring flange, said skirt having an annular skirt-extension of largeheat-carrying capacity that passes inside of said ringflange and Joins said skirt to said top portion, said skirt and its skirt-extension being spaced from said ring flange to leave an open space, said ring flange being Joined to said top portion bya section of metal that is markedly thinner than said top portion to keep small thethan the skirt metal and the upper one having 9.

lower thermal expansivity than the lower one, and both of said expansion-control bands being coated with a material that facilitates the slidof the skirt-metal on them.

' .5. A piston as set forth in claim 4, with the addition that said skirt-extension and the upper part of the cylinder-engaging part of the skirt are provided with a plurality of longitudinalpansivity than is the skirt-metal and that is slota.

o'rro oaa'rna BERRY. 

